The present invention relates to instrumentation and methods for visually recording the formation of stitches and recording certain characteristics of the threads in a sewing machine environment and particularly relates to instrumentation and methods for viewing loop formation under the throatplate of a sewing machine and transient tension characteristics of the thread as it is stitched into a fabric.
Repeatable and effective needle loop formation is mandatory for good sewability and very important in maintaining sewing efficiency. The size and shape of the needle loop formed and the angle that is formed by the thread in relation to the needle are characteristics that vary from one thread type to another. While needle loop formation is also dependent on other factors, skipped stitches will occur if the loop is not properly formed.
At present, the dynamic performance of threads in a sewing machine environment, particularly in the formation of stitches, has not been observed in view of the high-speed operation of the various elements which cooperate in the sewing machine to form the stitch in the confined area in which the stitches are formed. The physical properties of threads, of course, can be determined by their static properties. However, the success or failure of a particular thread in a sewing machine is determined not by static properties but by the dynamic properties of the thread and its ability to form proper loops. Under present conditions, a thread either breaks or not and a comparison of the performance characteristics of various threads in a dynamic sewing machine environment simply cannot be obtained. For example and as indicated previously, loop formation as part of the ultimate formation of a stitch is critical for performance and is not capable of being adequately predicted by the physical properties of the thread inasmuch as loop formation is a dynamic rather than static function.
Furthermore, thread tension while sewing is an important factor. Current practice is to set the tension while winding thread through the sewing machine at very low speed and assume that the tension increase at sewing speeds is the same for all threads. This, however, is quite unlikely. Difficulties have previously been experienced in measuring more than the average level of tension on the thread, i.e., the peaks and valleys of tension transients have not readily been ascertained.
According to the present invention, instrumentation is provided to observe and record various features of thread movement in the critical area of a sewing machine, that is, the area below the throatplate where the stitching, including loop formation, occurs. By being able to visually observe and record thread movement in this area, as well as to accurately record the magnitude of tension transients alone or in conjunction with the visual observation, it is possible to compare the performance of different types of threads. For example, with the instrumentation system of the present invention, flexibility, dynamic bending modulus, lubricity, stick slip, core versus wrapper problems, consistency, as well as range of movement, and effect of tension can all be examined in relation to the physical properties of the thread and its construction. Controlled and accurate fabric and thread feed will thus allow both repeatability and optimization. With respect to the measurement of tension transients, the present instrumentation is able to record, during the about seven millisecond needle stroke, tension transients which can be displayed on an oscilloscope or recorded on magnetic tape and analyzed.
According to the present invention, there is provided a fiberoptic bundle for reception in a guide path or guide way formed in the sewing machine bed whereby the end of the fiberoptic bundle terminates adjacent to or in the region to be observed. That is, the end of the fiberoptic bundle terminates adjacent the region of loop formation below the throatplate in the bed of the sewing machine. The fiberoptic bundle is multi-channelled and includes a pair of channels for transmitting light into the region to be observed. Because this region is substantially fully enclosed, an extremely high intensity of light is required, particularly considering the high frequency of the moving parts, on the order of 3,000 to 9,000 cycles per minute. Thus, a high intensity arc strobe light is coupled at the end of the fiberoptic bundle external to the sewing machine whereby stroboscopic light is transmitted through the fiberoptic bundle to illuminate the region desired to be observed. Another channel of the fiberoptic bundle transmits light from the region to a monitoring and recording system. For example, the monitoring system may include a low-light camera. Thus, by adjusting the frequency of the strobe light, the movements of the elements of the sewing machine including the threads for forming the stitch, can be observed, recorded, and played back more slowly.
It will be appreciated that, because of the nature of the stitching action, an accurate or complete observation of the stitch-forming process requires observation from at least two directions, preferably about 90.degree. apart, and preferably from three directions, whereby the opposite sides of the needle and thread carried thereby can be observed, as well as the action of the looper from a direction intermediate such opposite directions. The light guide pathways are therefore formed in the bed of the sewing machine to enable observations of the loop formed by the needle as it moves below the fabric, the loop capture by the looper, and their cooperation to form the stitching. Consequently, such guide ways or guide paths are preferably three in number, two 180.degree. apart and the third at 90.degree. relative to each of the other guide paths.
Preferably, a tension measuring load cell is secured to the side of the sewing machine. The thread passes over a pair of spaced pins between which is provided a cantilevered pin forming part of the tension measuring load cell. Because of the high frequency response of the load cell, tension transients may be measured and correlated with the movement of the thread as observed in the stitch formation region by the video camera.
Accordingly, and in accordance with one embodiment of the present invention, there is provided, in a sewing machine having a bed, a throatplate carried by the bed for receiving a reciprocable needle and thread carried thereby, and a mechanism disposed below the throatplate for cooperating with the needle and thread to form a stitch, apparatus for viewing the region of stitch formation in the bed below the throatplate comprising fiberoptic means carried by the bed for transmitting light into the region to be viewed and conveying light from the region. A strobe light is coupled to the fiberoptic means for periodically illuminating the region through the fiberoptic means. Means are coupled to the fiberoptic means for producing a dynamic image of the region illustrating the movement of the threads, needle and looper when forming the stitch.
Preferably, means for measuring tension transients on the thread during reciprocating motion of the needle carrying the thread are provided. Such means include a load cell having a cantilevered beam in contact with the thread and serving as an electromechanical transducer.
Accordingly, it is a primary object of the present invention to provide instrumentation and methods for determining the performance characteristics of thread in a sewing machine under dynamic operating conditions. It is also a feature of the present invention that the instrumentation is readily adaptable to the wide variety of existing sewing machines, with little or no modification to the machines and no interference with normal operation.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.